This invention relates to centrifugal type separators for removing moisture from a moisture laden gas stream consisting of such gases as digester gases, landfill gases and raw natural gases.
Digester gas is generated by digester sludge tanks of various types and sizes. This gas is a bi-product of the anaerobic digestion process of raw sludge from waste water treatment plants. Digester gas contains approximately 70% methane (CH.sub.4), 27% carbon dioxide (CO.sub.2) and about 3% of other gases. The gas carries with it not only moisture but various impurities such as dirt. Because of its high methane content, it is classified as a hydrocarbon fuel having a calorific value in the range of 16 to 22 kJ/cu. metre. The calorific value is dependent to some extent on the moisture content. The economic viability of the anaerobic digestion process is dependent upon the quantity and calorific capacity of the gas mixture produced by the process. By using a process that reduces the moisture content, the calorific value of the gas can be increased. Digester gas can be used as a fuel for firing boilers utilized for plant heating systems, to heat digesters, and to drive engine-driven generators used to produce electrical power.
An important factor that must be taken into account in the treatment and use of digester gas is that the gas can be explosive when it is in contact with air in a certain proportion (ie. in the range from 5:1 to 20:1).
It is known to use manual, mechanically operated moisture separators or drip traps in order to remove moisture and dirt from a moisture laden gas stream in order to increase its calorific value. However, such separators are plagued with several shortcomings and difficulties. Firstly, because of their lower efficiency in removing moisture, the resulting gas has a low calorific value and may even be unable to sustain a continuous flame. Moreover, generally there is a need for frequent attendance and maintenance of these separators. The potential for an explosion is significant and can arise from improper maintenance or even temporary lack of attendance. Further, there is a danger of moisture and dirt build-up in gas lines leading to possible flooding of control valves, flame arrestors, meters and other equipment, reducing accuracy of instrumentation, and creating a safety hazard.
In addition to these known separators, automatic continuous types of digester gas moisture separators have been used in the 1980's in North America. These separators are essentially gravity type separators with some inertial separation achieved by the addition of a deflector or baffle plate which changes the direction of gas flow. These separators which have a cylindrical body configuration have improved reliability of operation and are slightly more efficient at moisture separation. However, their efficiency is below 50% and their pressure losses are high due to low regain of static pressure. Their design tends to be rather crude and they lack the required features to enable efficient separation of moisture and contaminants from the gas stream.
It is an object of the present invention to provide an improved centrifugal-type separator providing more efficient removal of moisture from the gas stream, which in turn leads to increased calorific value of the digester gas.
It is a further object of the invention to provide a separator which can minimize attendance and maintenance of the separator. The preferred separators described herein can also prevent possible flooding of control valves, meters, flame arrestors and other equipment due to moisture build-up in gas lines. Also, these centrifugal-type separators can be made suitable for a variety of digester gas system layouts. They can be constructed for different capacities and for a variety of operating conditions, ranging from the simplest to complex, large systems.